The present invention relates to a plastic-encapsulated semiconductor device that is plastic-encapsulated at a portion thereof in which a semiconductor chip is mounted on a leadframe, and that exposes land electrodes each serving as an external terminal at the bottom surface of the device, and also relates to a leadframe used for the plastic-encapsulated semiconductor device.
In recent years, in order to cope with the downsizing of electronic equipment, high-density packaging of semiconductor components has been more and more required. In keeping with this trend, semiconductor devices are reduced not only in size but also in thickness. Furthermore, a variety of new ideas and new devices are being tested for the reduction of production cost and the improvement of productivity. Hereinafter, a conventional leadframe used for a plastic-encapsulated semiconductor device, and how the leadframe is formed will be described.
FIG. 12 shows the structure of a conventional leadframe used for a plastic-encapsulated semiconductor device disclosed in Japanese Unexamined Patent Publication No. 2001-77274. As shown in FIG. 12, the conventional leadframe includes: a die pad 1001 on which a semiconductor chip is to be mounted; suspension leads 1003 each having a tail end which is connected to an outer frame 1002 and a front end at which an associated one of four corners of the die pad 1001 is supported; and linear land leads 1004 and leads 1005 each having a front end facing the die pad 1001 and a tail end connected to the outer frame 1002. As used herein, “suspension lead” refers to a lead that is suspended between a die pad and an outer frame of a leadframe. The bottom portions of the land leads 1004 and leads 1005 each constitute an external terminal (land portion 1008). Each lead 1005 is formed so that, in addition to the bottom portion thereof, an outer lateral portion thereof constitutes an external terminal to be connected to a motherboard. Besides, the front end of each land lead 1004 is extended beyond that of each lead 1005 and is located closer to the die pad 1001.
The die pad 1001 is provided with an upwardly protruding circular protrusion 1006 located at an approximate center of the surface of the die pad 1001. The protrusion 1006 is formed by performing a pressing process in which a plate constituting the die pad 1001 is pressed so that the plate is half-sheared and is partially protruded upward. The protrusion 1006 substantially functions as a portion for supporting a semiconductor chip, and when a semiconductor chip has been mounted thereon, a gap is formed between the top surface of the die pad 1001 (except a region thereof at which the protrusion 1006 is formed) and the bottom surface of the semiconductor chip. At a region of the top surface of the die pad 1001 surrounding the protrusion 1006, a groove 1007 is provided. When a semiconductor chip, which has been mounted on the die pad 1001, is encapsulated with plastic encapsulant, the plastic encapsulant is allowed to get into the groove 1007.
With the use of the leadframe formed as described above, a semiconductor chip is mounted on the die pad, connected to each lead with a metal wiring, and encapsulated with plastic encapsulant, thereby forming a plastic-encapsulated semiconductor device. In the resulting device, the bottom surface of each land portion 1008 whose front end is curved is located at the bottom surface of the plastic-encapsulated semiconductor device, i.e., the bottom surface of the plastic package, and the bottom portion of each lead 1005 whose front end is curved is located outwardly of each land portion 1008 so that two rows of the external terminals are arranged in a zigzag manner. Thus, a Land Grid Array (LGA) package is provided.